Incidence of asthma and asthma-related disorders is increasing globally and in the developed world especially. According to a 2004 survey in the United States, asthma and related disorders resulted in almost 1.8 million emergency room visits, over 450,000 hospital admissions and 5,429 deaths. Asthma is directly responsible for approximately 15% of all pediatric emergencies (Cohn, Ann. Rev. Immunol., 2004; Barnes & Lemanske, New Engl. J. Med., 2001). The economic impact is high, estimated at ˜$16 billion per year. These figures have been rising over the last 20 years. Thus, asthma constitutes a significant and growing medical problem in the United States in terms of morbidity and economic impact.
Triggered by airborne antigens such as pollens, viruses, fungi and bacteria, asthma involves a complex network of cytokines (Walker et al. J. Allergy Clin. Immunol., 1991). Accumulation of Th2 cells in the lung tissue is a key feature of asthma (Robinson et al., New Engl. J. Med., 1992). In the course of asthma, multiple cytokines are released from various cell types (e.g., epithelial cells, lymphocytes, mast cells and granulocytes) in the lung parenchyma. The released cytokines help to initiate and maintain asthma development. In experimental asthma models, airway hyper-reactivity is accompanied by high levels of IL-4 and IL-5. IL-4 appears to be essential for the development of Th2 responses in general (Mowen & Glimcher, Immunol. Rev., 2004), and animals genetically deficient in IL-4 (i.e., IL-4 knock-out mice) cannot be induced to develop allergic airway inflammation (Ray & Cohn, J Clin Invest., 1999).
Other evidence, however, suggests that IL-13, and not IL-4, seems to be a key cytokine to asthma pathogenesis in humans. In humans, asthma-specific T-cells produce IL-13, and IL-13 elevates mast-cell proliferation and induce IgE synthesis (Punnonen et al., Proc Natl Acad Sci USA., 1993). Sputa obtained from asthma patients are rich in IL-13 (Berry et al., J Allergy Clin Immunol., 2004). IL-13 mRNA and protein are expressed at a high level in the lungs of trigger-exposed human volunteers and asthma patients (Humbert et al., J Allergy Clin Immunol., 1997). Airway hyper-reactivity accompanied by high levels of IL-4, IL-5 and IL-13 can be induced in normal but not IL-13−/− mice (Mattes et al., J. Immunol., 2001) Thus far, experimental therapeutic strategies to target Th2 cytokines which do not address IL-13 have failed (O'Byrne, Chest, 2006). Asthma-sensitized animals can be protected by blocking the cell-surface receptor for IL-13 (Taube et al., J Immunol., 2002). IL-13 appears to be a contributing factor in the increased IL-4 and IL-5 levels. Once initiated, elevated levels of IL-4 and IL-5 are believed to exacerbate the asthmatic response.
An attempt was proposed to use IFN-λ in order to alleviate asthma. To this end, Davies et al. (WO 2007/029041) disclose the use of IFN-λ in virus-induced exacerbation of asthma. An aerosolized dose is recommended to bring IFN-λ in direct contact with the virus-infected airway epithelial cells. This group hypothesized that IFN-λ would eradicate the viral infection, thus alleviating the virus's ability to exacerbate the asthma. Viruses (such as respiratory syncytial virus (RSV) and rhinovirus (RV)) are known to infect airway epithelial cells, and the anti-virus effect of IFN-λ is believed to be maximized by the proposed airway delivery of IFN-λ. The half-life of IFN-λ may hinder the approach, as attempts are made to couple the IFN-λ with polyethylene glycol (PEG) to extend its functional half-life and to present an alternative method of introducing IFN-λ, other than through expression of DNA constructs. However, the airway route does not guarantee IFN-λ to come in contact with cytokine-producing lymphoid cells in lung parenchyma. The presence of an exceedingly thick mucus layer in asthmatic patients further hinders the success of this approach. While Davies et al. proposes a direct anti-virus effect by IFN-λ, the possible role of IFN-λ with Th2 cells in the lung, blood and lymphoid compartments and their secreted products (i.e., IL-4, IL-5, IL-13 cytokines, etc.), has not been addressed.
Intravenous delivery of IFN-λ is undesirable. Once administered, circulating IFN-λ may exert global side-effects on a human body. In addition, Th2 cytokine-producing cells in the lung parenchyma may be shielded from the systemic levels of IFN-λ. It is generally believed that intravenous administration IFN-λ is not ideal to combat asthma.
There is a continuing need to find an effective means to modulate Th2 cells in an attempt to blunt cytokine production. The present inventors surprisingly found that IFN-λ can directly modulate Th2 cells in affecting the cytokine release. Specifically, the present inventors discovered that ex-vivo treatment of peripheral mononuclear cells (including naïve and memory T-cells) blunts the production of IL-4, IL-5 and IL-13. Given that these cytokines contribute to an asthma response, the present inventors propose a method of alleviating asthma by ex-vivo treatment of human blood leukocytes with IFN-λ, followed by its administration into a human. It is believed that administration of IFN-λ-treated blood leukocytes will inhibit the human body from generating asthma-inducing Th2 cytokines, and thus alleviating the symptoms and root-cause of asthma.